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Storage guide · AS/NZS 4534:2006 Appendix D

White spots on your brand-new fence?
It's called white rust — and it starts in the shed.

Your wire didn't fail. The storage did. Here's the 1-minute version of how galvanised and Zn/Al-coated fencing wire goes from shiny-silver to chalky-white — and the simple setup that prevents it.

The 30-second answer

The trigger Damp, still air around the coil. Tarp on top, concrete underneath. →
What happens Moisture wicks between turns. Zinc oxide forms instead of the protective carbonate film. →
The fix Off the ground. Open air. Indoors if you can. Keep humidity under 70%.

So… what actually is white rust?

Same chemistry as the protective grey patina you want — just the wrong kind, formed under the wrong conditions.

moisture Wire coil cross-section
The plain version

Fresh zinc wants to react with carbon dioxide in dry air. That reaction builds a thin, tough layer of zinc carbonate — the matte grey colour you see on healthy old galvanised wire. That layer is what makes the coating last 20+ years.

But if the wire is damp before that layer can form, the zinc reacts with water instead. You get zinc oxide / hydroxide — a porous, chalky deposit that holds moisture against the metal instead of protecting it.

That's white rust. And once it starts, the coating keeps wetting, keeps reacting, and keeps thinning.

Honest note: A bit of white rust on the surface usually doesn't ruin the wire — but if storage stays bad for weeks or months, it eats into the zinc you paid for. The good news: it's almost always preventable.

The 4 storage sins

If you're doing any of these — even one — white rust is coming.

✕
🏕️

Wrapped in tarp or plastic

Sealed sheeting traps moisture and kills airflow. The coil "sweats" overnight.

✕
🧱

Sitting on concrete or dirt

Concrete wicks groundwater up. Damp surface = capillary moisture into every turn.

✕
📦

Touching cardboard, paper or fresh timber

They hold moisture and leach chemicals (especially CCA-treated or termite-proofed timber).

✕
⚗️

Stored near fertiliser or fungicide

Ammonia, chlorides and sulphates corrode zinc fast. Don't share a shed with the chem stack.

The boring storage that actually works

Four small habits. That's the whole secret.

vent vent off ground RH < 70% dry air, free flow ☀️
✓
Up off the ground Timber racks, pallets, even bricks — anything that breaks contact with the floor and lets air pass underneath.
✓
Indoors, with airflow A dry shed beats a yard. A vented shed beats a sealed one. Open the doors when the temperature swings.
✓
No tarps, no plastic wrap If you must cover, use breathable cloth and leave a gap. Sealed plastic is the single most common cause of white rust.
✓
Keep chemicals away No fertiliser, fungicide, lime, or fresh CCA timber in the same room. Different shed if you can.

The one number to remember

70% RELATIVE HUMIDITY

Below 70% RH in clean air, zinc corrodes very slowly — practically not at all. Above it, the protective carbonate layer can't form properly and white rust starts winning.

A $15 hygrometer in the shed tells you everything you need to know. If the needle stays under 70 most of the year, you're fine. If it climbs, ventilate or move the coils to a drier spot.

"My wire turned grey — is that bad?"

Short answer: that's the good kind.

shiny
new
dull
silver
deep
grey

Lustrous silver → dull → grey is normal aging

Zinc reacts with CO₂ over time and forms a tough, dark patina. The colour change has nothing to do with damage — in fact it means your protective layer is doing exactly what it should. Don't confuse it with white rust, which is chalky, powdery, and only forms when storage went wrong.

Buying for a humid site or coastal yard?

We can ship coils with wax / chromate passivation for extra storage tolerance, or pair you with Zn/5% Al alloy wire that handles wet conditions far better than plain galv.

Email us for a spec More technical guides

Source: AS/NZS 4534:2006 — Appendix D (Informative). This summary is provided by YIELD MAX for planning purposes; the published standard remains the authoritative reference.